White Paper:
Understanding the Harmonic Analysis Report
Figure 1. Right click on
the graph to generate a
report.
Contributed by Ben Bowman August 2013
ABSTRACT
Harmonics are distortions in the 60Hz voltage or current
caused by non-linear loads on the system. Harmonics
are of interest to utilities as they can cause damage
to equipment, such as creating extra vibrations in
motors or causing excess heat in transformers. Power
Monitors, Inc. (PMI) ProVision software features
advanced harmonic analysis features. One such
feature is the ability to generate harmonic analysis
reports. This paper will examine how to create a
harmonic report in ProVision, describe the various
pieces of the report, and also discuss when to use this
report vs. other ProVision harmonic tools.
Opening a Harmonic Report
The Harmonic Report is the tabular version of
the Harmonic Graph in ProVision. This harmonic
information is calculated by ProVision from raw
waveform data captured by the recorder. While the
harmonic bar chart in the graph is useful for spotting
patterns and getting a quick overview, the harmonic
report is better for a more detailed analysis.
Report Header
To see the Harmonic Report, it is necessary first to
select the harmonic analysis via the graph. Once you
have loaded a recording file, go to the main toolbar
and click on “Graph”. In the drop down that appears
click on “Harmonic Analysis” and “Magnitudes”. The
harmonic analysis is computed by ProVision for the
cycle shown in the grey rectangle at the top of the
graph. Click and drag the rectangle to cover the cycle
to analyze; ProVision will recalculate the harmonics as
it moves. For harmonics, a “normal” cycle should be
selected, so representative steady-state harmonics
are computed, not the harmonics of a disturbance
(unless that’s really what’s needed). Once positioned,
right click on the graph that appears on the section
that you wish to generate a report from, in this example
we will right click on the Volts bar graph and select
“Launch Report” (Figure 1).
The report starts with the basic header information at
the top of every ProVision report, such as the recorder
used to make the recording, and the firmware and
software currently installed on it. Next is additional
information about the recorder, and the recording
interval used.
Next is the specific data source selected in the grey Figure 2. Detail from
box on the graph screen (Figure 2). In this example, Waveform #5
A detailed report of harmonics present in the recording
will appear. This report is a textual representation of the
previous graph. The report can be exported to several
formats, including CSV, by right clicking on the body
of the report. There are several sections to the report,
which we will discuss in turn. The sections are a report
header, a section on Total Harmonic Distortion (THD)
and other distortion measures, Harmonic Magnitude,
and lastly a section on Harmonic Phase Angle.
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White Paper:
Understanding the Harmonic Analysis Report
waveform capture #5 is used, and the cycle under the most useful measurement especially when there
analysis starts at point 234, 15.17 ms into the waveform. is high harmonic content. The THD-R measurement
can be prone to misinterpretation, which can easily
The next section (Figure 3) is a block of statistics lead to measurement errors when measuring larger
computed from the harmonic data, including several distortions.
THD measurements, TIF, and K-Factor values in this
table are percents, with two main categories, THD THD Fundamental
Fundamental and THD RMS. These terms are defined Total Harmonic Distortion in reference to (F)
Fundamental, represents the ratio, in percent, of
here:
the voltage/current harmonic components relative
THD-F and THD-R
to the voltage/current of the fundamental. When the
There are two typical definitions used when dealing reference is not indicated (i.e. simply THD), then it is
with Total Harmonic Distortion. The two types of Total usually assumed the reference is fundamental. For
Harmonic Distortion are THD-F and THD-R. They both power systems, THD-F is by far the best measurement
are figures of merit used to quantify harmonic levels to use.
in voltage and current waveforms; however, each one
Figure 3. Block of uses a different reference. THD-F is a comparison to THD-R
statistics computed from the fundamental and THD-R is a comparison to the Total Harmonic Distortion in reference to (R) RMS, is
harmonic data signal’s RMS value. For power systems, the THD-F is the ratio, in percent, of the voltage/current harmonic
components relative to the absolute voltage/current
RMS. Because this is related to an RMS base, all
harmonic values must be calculated in RMS. Since
no harmonic, or the fundamental, can be larger than
the entire RMS value, the THD-R value can never be
greater than 100%. In cases of large distortion, the
value approaches 100%, and it is more difficult to
distinguish similar readings, compared to the THD-F
value (which can exceed 100%).
THD is further classified on the report as odd, even,
and triplen harmonics. Even harmonics are simply
the even number harmonics; harmonics 2, 4, 6, etc.
Odd harmonics are the odd numbers, not including
the 1st harmonic (the fundamental). Most loads create
more odd harmonics than even harmonics. Triplen
harmonics are odd multiples of the third harmonic.
Even Harmonics
While inspecting a sinusoidal wave, if both the upper
half and the lower half of the wave are symmetrical,
then no even harmonics are present. An asymmetrical
wave indicates the presence of even harmonics. Even
harmonics are an indicator of an unusual load in the
system. Even Total Harmonic Distortion should be
close to zero in a normal system. If the THD of even
harmonics is a significant part of the total, further
investigation is warranted.
Odd Harmonics
Odd harmonics make up most harmonic currents found
in distribution systems. Of particular interest are the
5th and 11th harmonics. The 5th and 11th harmonic
have a negative sequence, and when applied to some
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White Paper:
Understanding the Harmonic Analysis Report
three-phase motors, they will try to run the motor
backwards. A major source of the 5th, 7th, and 11th
harmonics is 6-Pulse variable frequency drives (see
the PMI white paper: Monitoring Variable Frequency
Drives for more information).
audible range and are based on the response of the
human ear. The higher the factor the more interference
is being generated. Other forms of communication,
besides telephones, are also affected.
Figure 4. Harmonic
magnitudes are broken
down by frequency in the
Magnitude section of the
report.
K Factor
Triplen Harmonics
Triplens are especially detrimental to grounded-wye
systems with current flowing through the neutral.
Normally balanced wye current cancels out in the
neutral, but triplen harmonics add together in the
neutral instead of cancelling. This can overload
the neutral and cause excessive heating. Devices
sometimes malfunction because the line-to-neutral
voltage is badly misshapen by the triplen harmonic
voltage drop in the neutral conductor.
Telephone Interference Factor (TIF)
K Factor is a measurement of current harmonic
distortion used in rating transformers. It’s used in
calculating the value necessary to de-rate a transformer
for harmonics. Harmonic current flow in a transformer
causes increased heating (due to various losses in the
core). Some of these losses increase linearly or even
more than linearly with the harmonic number.
Magnitude
In the magnitude section of the report, harmonic
magnitudes present in the cycle are broken down
by frequency as shown in Figure 4. Amounts are
represented in real units, i.e. voltage magnitude is
represented in volts present in each channel, while
current is represented as amps. The frequency and
harmonic number are both shown.
TIF is a measure of the potential telephone noise
caused by the harmonic distortions from a power system
on nearby telephone equipment. It is a dimensionless
quantity that depends upon a weighting factor derived
from 1960 weighting curve by the Edison Electric
Institute. This weighting factor is weighted heavier In addition, the real power at each harmonic is shown,
on frequencies that tend to cause interference in the computed by taking the product of harmonic voltage
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White Paper:
Understanding the Harmonic Analysis Report
and current, and the cosine of the phase angle to record as stripcharts. The waveform-based method Figure 5. Phase angles
has the advantage of showing all harmonics, and with for each voltage, current,
between them.
much less memory cost. It’s also useful for harmonic and power harmonic
Phase
analysis of an existing recording, where no harmonics
Phase measures the offset between each phase of were explicitly enabled. For a detailed explanation of
power, in degrees. The phase angle for each voltage, the strategies for using waveform capture for harmonic
current, and power are shown after the magnitudes analysis in ProVision, see the white paper Harmonics
(Figure 5). The channel 1 voltage fundamental is used From Periodic Waveform Capture.
for the phase angle reference for all harmonics and
voltage and current channels. The power phase angle Conclusion
is the phase difference between current and voltage at The Harmonic Analysis Report is a powerful tool
featured in PMI ProVision. It features a plethora of
that frequency.
detailed data, presented in an easy to read format.
Harmonic Report vs. Stripchart
In addition, the data can be exported to CSV and a
ProVision also features harmonic stripcharts, which number of other formats.
allow for long-term study of harmonics. An important
difference between a harmonic stripchart and a Ben Bowman
harmonic report is that a harmonic report only shows Web Software Developer
harmonics for a one-cycle period. A harmonic stripchart [email protected]
may be more suited for a long-term trend study of www.powermonitors.com
harmonics present in a system, but requires more 800.296.4120
recorder memory, and selection of specific harmonics
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